Partitioning and transport of hydrocarbons from crude oil in a sand and gravel aquifer

Hydrocarbons in crude oil are partitioned in water and sediment based on the solubilities and sorptive properties of individual compounds. Crude oil from a pipeline break accumulated as an oil body at the water table, 6 m below land surface, in a glacial outwash aquifer near Bemidji, Minnesota. The crude oil was a paraffinic oil composed of about 60% saturated hydrocarbons, 33% aromatic hydrocarbons, and 6% resins and asphaltenes. The aromatic hydrocarbons from C6 to C10 are soluble in water and are transported downgradient farther than other organic compounds. The higher molecular-weight hydrocarbons are predominantly normal alkanes in the C11 to C33 range and the isoprenoid hydrocarbons, pristane and phytane. These hydrocarbons are insoluble and occurred in ground water only near the soil source, and not downgradient. However, normal alkanes were found on sediment 30 m downgradient, which suggests that they are transported as an oil film at the saturated/unsaturated zone interface